The
Neutron EDM
Experiments
at the ILL
Philip Harris
University of Sussex
(for the EDM Collaboration)
Highlights
1. nEDM “Classic”
New (but preliminary) limit:
|dn| < 3.1 x 10-26 e.cm
2. CryoEDM
Under development:
100x improved sensitivity
P. Harris
University of Sussex
Electric Dipole Moments

Separation between
+,- charge centres
E

EDMs are



+
P odd
T odd
Complementary approach
to study of CPv
d n = dn s
P. Harris
University of Sussex
CP violation & the neutron EDM

SM EDM predictions very small...


Beyond SM predictions typ. 106 greater



... so no SM background to worry about
... so EDMs are excellent probe of BSM CPv
SM parameterisation of CPv inadequate
to explain baryon asymmetry
Strong CP Problem: s < 10-10 rads
P. Harris
University of Sussex
Implications for SUSY
q
squark
g
gaugino
q
q
squark
g
gaugino
q
quark color dipole moments
quark electric dipole moments
CP phase from soft breaking
naturally O(1)
naturally ~ a/p
m
(loop factor)  2q sin CP
2
scale of SUSY breaking naturally ~200 GeV L
c
d q, d q ~
c
du,d, du,d ~
31024 cm naturally
n and Hg experiments give du< 2  1025
dd< 5  1026
dcu< 3  1026
dcd< 3  1026
~ 100 times less!
L > 2 TeV ? CP < 10-2 ?
P. Harris
University of Sussex
History
Factor 10
every 8 years
on average
Now
CryoEDM
P. Harris
University of Sussex
Measurement principle
Use NMR on ultracold neutrons in B, E fields.
B0
B0 E
B0 E
<Sz> = + h/2
h(0)
h()
h()
<Sz> = - h/2
() – () = – 4 E d/ h
assuming B unchanged when E is reversed.
Energy resolution of our detector: 10-21 eV
P. Harris
University of Sussex
Apparatus
HV
feedthru
Neutron
storage
chamber
B-field
coils
P. Harris
University of Sussex
nEDM measurement
Look for n freq changes correlated with changes in E
29.9295
Neutron resonant frequency (Hz)

29.9290
29.9285
29.9280
29.9275
Electric Field
+
-
29.9270
29.9265
29.9260
0
5
10
15
Run duration (hours)
25
P. Harris
University of Sussex
20
Mercury co-magnetometer
Compensates B drift...
Mercury frequency (Hz)
7.7890
7.7888
7.7886
7.7884
7.7882
0
5
10
Run duration (hours)
15
P. Harris
University of Sussex
20
nEDM measurement
Precession frequency (Hz)
29.9295
Raw neutron frequency
Corrected frequency
29.9290
29.9285
29.9280
DB = 10
-10
T
29.9275
29.9270
29.9265
29.9260
0
5
10
15
Run duration (hours)
P. Harris
20
25
University of Sussex
Neutron EDM results (binned)
10
Current limit
set here
8
6
EDM (10-25 e.cm)
4
2
0
500
-2
700
900
1100
1300
1500
1700
1900
2100
-4
-6
-8
Stat. limit now
1.54 x 10-26 e.cm
-10
P. Harris
University of Sussex
Systematics

Consider
 n g Hg
R

 Hg g n



Should have value 1
R is shifted by magnetic field gradients
Plot EDM vs measured R-1:
P. Harris
University of Sussex
Systematics
150
Magnetic field down
EDM (10-25 e.cm)
100
50
0
-40
0
-20
20
40
-50
-100
-150
R-1 (ppm)
B

z
P. Harris
University of Sussex
Systematics
150
Magnetic field up
EDM (10 -26 e.cm)
100
50
0
-10
0
10
20
30
40
-50
-100
-150
R-1 (ppm)
B

z
P. Harris
University of Sussex
Geometric phase
J.M. Pendlebury et al.,
PRA 70 032102 (2004)
Two effects:
B
 Br  r
z
and, from Special Relativity, extra
 motion-induced field

1 vE
B 
g c2
P. Harris
University of Sussex
Geometric phase
Bnet
Br
Bnet
Bv
Bottle
(top view)
Bv
... so particle
sees additional
rotating field
Frequency shift
E
Looks like
an EDM
Bnet
Bv
Br
Bnet
P. Harris
University of Sussex
150
100
100
50
0
-10
0
10
20
-50
B up
0
-40
-20
0
20
-50
-150
-150
R-1 (ppm)
R-1 (ppm)
The answer?
R-1
0
B down
40
50
-100
-100
EDM
30
EDM (10-25 e.cm)
EDM (10 -26 e.cm)
Results
150
Nearly...
P. Harris
University of Sussex
40
Results
EDM
B up
0
Small dipole/quadrupole fields
can pull lines apart
& add GP shifts
R-1
B down
P. Harris
University of Sussex
Results
EDM
B up
Small dipole/quadrupole fields
can pull lines apart
& add GP shifts
R-1
0
B down
Measure and
apply correction
...difficult!
P. Harris
University of Sussex
Error budget
Statistical
Dipole & quadrupole shifts
Enhanced GP dipole shifts
(E x v)/c2 from translation
(E x v)/c2 from rotation
Light shift: direct
B fluctuations
E forces – distortion of bottle
Tangential leakage currents
AC B fields from HV ripple
Light shift: GP effects
1.54E-26 e.cm
6E-27 e.cm
~4E-27 e.cm
1E-27 e.cm
1E-27 e.cm
8E-28 e.cm
7E-28 e.cm
4E-28 e.cm
1E-28 e.cm
<1E-28 e.cm
P. Harris
8E-28 e.cmUniversity of Sussex
PRELIMINARY Results
dn = (-0.31  1.54  1.00) x 10-26 e.cm
New (preliminary) limit:
|dn| < 3.1 x 10-26 e.cm (90% CL)
Preprint expected soon
P. Harris
University of Sussex
CryoEDM
Dispersion curve for free
neutrons
Landau-Feynman
dispersion curve for 4He
excitations
ln = 8.9 Å; E = 1.03 meV
R. Golub and J.M. Pendlebury
Phys. Lett. 53A (1975),
Phys. Lett. 62A (1977)
•More neutrons
•Higher E field
•Better polarisation
•Better NMR time
100-fold improvement in sensitivity!
P. Harris
University of Sussex
CryoEDM overview
Neutron beam input
Cryogenic
Ramsey chamber
Transfer section
P. Harris
University of Sussex
Cryogenic Ramsey chamber
HV electrode
Superfluid He
n storage cells
P. Harris
University of Sussex
CryoEDM
Turns on
October 2006
P. Harris
University of Sussex
Conclusions
100
EDM (10 -26 e.cm)

150
10
8
50
0
-10
0
10
20
30
40
-50
6
-100
4
-150
R-1 (ppm)
2
0
500
-2
700
900
1100
1300
1500
1700
1900
2100
150
100
-4
-6
-8
-10
EDM (10-25 e.cm)

EDM “Classic”: new (preliminary) limit, factor
2 improvement
CryoEDM coming soon – 100x more sensitive
Watch this space!
EDM (10-25 e.cm)

50
0
-40
-20
0
20
-50
-100
-150
R-1 (ppm)
P. Harris
University of Sussex
40